JPH01225790A - Zn-ni alloy plated steel sheet having superior press workability and characteristic after coating - Google Patents

Abstract

PURPOSE:To improve press formability and various characteristics after coating by forming a Zn-Ni alloy plating layer consisting of a first layer having a specified low Ni content and a second layer having a specified high Ni content and specifying the amts. of the layers. CONSTITUTION:This Zn-Ni alloy plated steel sheet has a Zn-Ni alloy plating layer having a two-layered structure consisting of a first layer contg. 3-10wt.% Ni and a second layer contg. 11-20wt.% Ni on a steel sheet. The total amt. of the first and second layers is 10-80g/m<2> and the ratio between the first and second layers is 1:(0.05-1). A zinc phosphate crystal layer contg. 3-10wt.% Ni and/or P as a third layer may be formed on the second layer by 0.1-4.0g/m<2> so as to provide a three-layered structure. The plated steel sheet has superior press workability, resistance to exfoliation by shock, adhesion to paint, resistance to swelling of a paint film from a scratched part after coating and resistance to formation of red rust.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention focuses on press workability and post-painting properties, that is, impact peeling resistance, paint adhesion, paint blistering on the eaves after painting,
This invention relates to a Zn-Ni alloy plated steel sheet that has excellent corrosion resistance against red rust and the like.

[Prior Art] In general, Zn-Ni alloy-plated steel sheets have superior corrosion resistance (corrosion resistance) in an unpainted state compared to pure Zn-plated steel sheets, and are therefore widely used, including for automobiles. It has been said that the optimal Ni content in this case is 10 to 15 wt%.

In recent years, Zrr-Ni alloy plated steel sheets have come to be used on the outer surface of automobile bodies to prevent so-called external rust, such as rust from defective parts of the coating film and blistering of the coating on the outer surface of the automobile body.

In this way, for applications where Zn-Ni alloy plating is used on the external surface, various properties after painting, such as paint film adhesion, impact peeling resistance against collisions with flying stones, etc., and from the edge of the defective part of the paint film, are important. It must have excellent corrosion resistance against red rust and paint blistering.

That is, when the present inventor investigated the suitability of Zn-Ni alloy plated steel sheets for use on the outer surface of automobile bodies, it was found that conventional Zn-N with a Ni content of 10 to 5 wt%
I-based alloy plated steel sheets cannot be said to have good impact peeling resistance, paint defects in outdoor exposure tests, and outer layers from the edge surfaces, etc. From this perspective, on the other hand, Ni content of 3 to 1
It was found that a Zn-Ni alloy plated steel sheet with a low content of 0 wt% was better. However, this Ni content is 3~
When a lowt% Zn-Ni alloy plated steel sheet was actually pressed to be applied to the outer panel of an automobile body, cracks occurred, and the conventional Ni content of 10 to 15vt% was applied.
It was found that the press workability was inferior to that of the Zn-Ni alloy plated steel sheet. The reason for this is that the Zn-Ni alloy plating layer with a Ni content of 3 to towt% is
Since it is softer than a Zn-Ni alloy plating layer with a content of 10 to 15 wt%, the plating layer may peel off (flaking) due to sliding between the plating layer and the mold during press processing.
This is because this caused mold galling and increased sliding resistance, which adversely affected the formability of the steel plate. In addition, the peeled plating layer sticks to the mold, increasing the frequency of mold cleaning and causing press defects called stars or pimples.

[Problems to be Solved by the Invention] As explained above, the present invention is based on the problems of conventional Zn-Ni alloy plated steel sheets and various investigations conducted by the present inventors, and the present invention is based on the fact that the Ni content is 3 to 10 wt%. In order to solve the press workability problem of the Zn-Ni alloy plating layer of By providing a plating layer, we developed a Zn-Ni alloy-plated steel sheet that has excellent press formability and various properties after painting.

[Means for Solving the Problems] The Zn-Ni alloy coated steel sheet having excellent press workability and various properties after painting according to the present invention has the following features: (1) Ni3 to lowt% as a first layer on the steel sheet; a Zn-Ni alloy plating layer containing
The layer has a two-layer structure of a Zn-Ni alloy plating layer containing 11 to 2 wt% Ni, and the ratio of the amount of the first layer to the amount of the second layer is 1:0.05. 〜l, and furthermore, the total plating amount of the first layer and second layer is 10 to 80 g/
The first invention is a Zn-Ni alloy coated steel sheet with excellent press workability and properties after painting, which is characterized by a thickness of 1.5 mm, and (2) Ni3~lowt% as a first layer on the steel sheet. a Zn-Ni alloy plating layer containing
As a layer, a Zn-Ni alloy plating layer containing 11 to 20 wt% of Ni, and on top of that, as a third layer, a deposited amount of 0.1 to 4.0 g/ is one or two types of N15P 3 to It has a three-layer structure of zinc phosphate crystal layers containing 10 wt%, and the ratio of the amount of the first layer deposited to the amount of the second layer deposited is 1:0.05~! and, furthermore, the first
A second invention provides a Zn-Ni alloy coated steel sheet with excellent press workability and properties after painting, characterized in that the total coating weight of the layer and the second layer is 10 to 80 g/m''. Consists of two inventions.

It is.

The Zn-Ni alloy plated steel sheet (hereinafter sometimes simply referred to as the steel sheet according to the present invention) having excellent press workability and properties after painting according to the present invention will be described in detail below.

First, like the steel plate according to the present invention, [Ni content 2 to 9 wt%, (η + γ) two phases consisting of 0, 05 to 2
[μm], the first layer of Zn-Ni alloy plating, [Ni content: 10-20ψt%, γ single phase, 0, 2-IOμm]
It has a two-layer structure with the second layer of Zn-Ni alloy plating with a high
JP-A-58-1999 discloses a zinc-nickel alloy coated steel sheet with excellent adhesion after processing so that the adhesiveness becomes 0.
006995 (hereinafter simply referred to as the publication) and the steel plate according to the present invention will be explained.

The steel sheet according to the present invention has some overlap in the Ni content of the first layer and the second layer when compared with the published publication, but the coating amount of the plating layer of the first layer and the second layer is different in the steel sheet according to the present invention. 1 : 0.05 to 1, with the first layer being the main component, whereas in the published publication, l : 5 to 100, the second layer is the main component, and the plating adhesion is completely incompatible. It's different. This is because the purpose of the steel sheet according to the present invention is different from that of the published publication. Namely, in the steel sheet according to the present invention, paint blisters and red rust occur from the bottom and end surfaces of the paint film after painting. This is to improve the corrosion resistance and impact peeling resistance after painting, and in the publication, it is simply to improve the corrosion resistance when unpainted.

Both post-coating corrosion resistance and naked corrosion resistance are corrosion resistance, but the corrosion mechanism differs depending on the presence or absence of a coating film. That is, the corrosion reaction is an anode reaction M->M""+ne (M is a metal element) a cathode reaction H, O+1/20t+2e-20H-
Corrosion progresses as a result of the occurrence of equal amounts of metal ions, but in materials without a coating, the metal ions generated by the anode reaction and the hydroxyl groups generated by the cathode reaction easily mix to form metal hydroxides. The difference in local pH of the surface is not large.

On the other hand, when a coating film is present, the bottom of the coating film becomes an anode and metal ions are generated, which generate hydrogen ions through the following hydration reaction and become strongly acidic.

M"+H20→M(OH),+nH" On the other hand, the area under the coating around the eaves becomes a cathode and becomes strongly alkali.

These alkali parts, strong acids in the cathode part, and strong alkali are difficult to mix with each other in the presence of a coating film, and local pH
The large difference between the two will not be resolved.

In this way, the presence or absence of a coating film greatly changes the environment where the corrosion reaction actually occurs, especially the PT (PT). Therefore, a material with good corrosion resistance may not necessarily be corrosion resistant after coating. Something bad happens.

The above explanation also applies to the Zn-Ni alloy plating layer, and in terms of bare corrosion resistance, Zn-N 1 (1
The corrosion resistance after painting of the steel sheet according to the present invention is good when the Zn-N1 (3 to Lht%) alloy plating layer is the main component. It becomes good when it becomes.

In addition, in the steel plate according to the present invention, by providing the first layer and the second layer as described later, the impact peeling resistance after painting is much better than either the first layer single layer or the second layer single layer. This is also superior to that shown in the published publication.

Next, each structure of the Zn-Ni alloy plated steel sheet having excellent press workability and properties after coating according to the present invention will be explained.

The first layer on the steel plate is a Zn-Ni alloy plating layer with a Ni content of 3-lowt% to maintain good corrosion resistance after painting. If the humidity is high in an environment like this, the paint film will swell from the bottom of the paint film, and if the Ni content exceeds lht%, red rust will occur from the bottom of the paint film in relatively dry environments such as outdoor exposure. Therefore, for parts that are painted and used, such as the outer surface of automobile doors, the Ni content of the Zn-Ni alloy plating layer has good bare corrosion resistance.
A Ni content of 3 to 10 wt% rather than 15 wt% is better from the viewpoint of corrosion resistance.

In addition, this Zn-Ni alloy plating layer with a Ni content of 3 to 10 wt% is a Zn-Ni alloy plating layer with a Ni content of 10 to 15 wt%.
- Since the Ni-based alloy plating layer is not hard, it is difficult to resist coating and peeling of the underlying plating layer due to chipping caused by flying stones when driving on the road, that is, impact peeling resistance after coating. Zn with a Zn content of 10 to 15 wt%
- Better than Ni-based alloy plating layer.

Therefore, the Zn content of the first Zn-Ni alloy plating layer is 3 to LOwt%.

However, since the Zn-Ni alloy plating layer containing m3 to lowt% of Zn is soft, during press molding, the plating layer may peel off due to sliding between the mold and the plating layer, causing the mold to seize. This impairs the formability of the steel sheet, increases the frequency of mold maintenance, and causes defects such as stars or pimples due to flake residue.

In order to solve this problem in the first layer, Zn-containing 13-1
On top of the 0wt% Zn-Ni alloy plating layer, a second layer of Zn-Ni alloy plating layer, which is harder than the Zn-Ni alloy plating layer, is provided.

In order to make the hardness higher than that of the first layer, the Ni content is changed to If~
2 (ht%), it is necessary to use a Zn-Ni alloy plating layer, and by setting the Ni content to 11wt% or more, the water-resistant adhesion of the coating film will be good, and the corrosion resistance, especially after painting, will be improved. Ni content is 20wt to improve corrosion resistance.
%, there is a clear tendency for deterioration.

Therefore, the Ni content of the second Zn-Ni alloy plating layer is 11 to 20 wt%.

The ratio of the adhesion amount of the first layer and the second layer described above needs to be equal to or higher than the second layer from the viewpoint of corrosion resistance, and also from the viewpoint of press formability. from the second
The amount of adhesion of the layer must be more than Ig/m', otherwise the peeling resistance (
It has little effect on improving flaking properties).

Furthermore, in the steel sheet according to the present invention, the Ni content is 3
~10 wt% of the first layer of Zn-Ni alloy plating layer, N
By creating a two-layer structure in which the second layer is a Zn-Ni alloy plating layer with an i content of 11 to 20 wt%, the impact peeling resistance after coating is improved.
It is important that the performance is much better than that of a Ni-based alloy plating layer.

This will be explained in more detail with reference to FIG.

Figure 1 shows that the first layer is a Zn-Ni alloy plating layer with a Zn content of 9 wt%, and the second layer is a Zn-based alloy plating layer with a Zn content of 13 wt%.
The adhesion amount of each of the two n-Ni alloy plating layers is
This figure shows the results of an experiment on changes in impact peeling resistance after coating when the total amount of two layers deposited was varied in various ways under constant conditions of 20 g/m''.

This impact peeling resistance is 7.9 to 11.1 mm in diameter at -20°C after applying 3 coats for automobiles to a steel plate.
100 g of granite with a diameter of mm was sprayed at an air pressure of 4 kg/cm'', and evaluation was made based on the maximum peeling diameter of the coating around the flaw.

In this case, the reason why the test is conducted in an environment of -20°C is because the coating film hardens at low temperatures, so the peeling diameter of the coating film becomes larger compared to the test at room temperature.
- For Ni-based alloy plating layers, peeling usually occurs at the interface between the plating layer and the base steel sheet.

When the second layer coating amount is t −t Og/m'' and the ratio of the second layer to the first layer is in the range of 0.05 to 1.0, the impact peeling resistance after coating is is 13wt% Z
Single layer of n-Ni alloy plating layer and Zn-containing layer are 9w
It can be seen that the impact peeling resistance after coating is good even when compared with a single layer of Zn--Ni alloy plating layer of t%.

The reason for this is not necessarily clear, but by creating a two-layer structure with different hardnesses of the plating layers, the interface between these two layers causes destruction preferentially, which alleviates the impact force applied to the coating film. This is also thought to be a factor.

Therefore, the ratio of the first layer adhesion amount to the second layer adhesion amount is l:Q,
05~l.

The total amount of the first layer and the second layer must be at least tog/ from the viewpoint of corrosion resistance as a paint base for automobiles, etc. Also, if the amount of adhesion is too large, ZnNi alloy Since the layer is flat, the peeling of the plating layer during processing increases significantly, and the hard plating layer restricts the deformation of the base plate, deteriorating the formability of the steel sheet itself, so the amount of adhesion is 80g/ m2 or less.

The two-layer plating described above has excellent press workability, but on top of this, a zinc phosphate treatment layer is added in an amount of 0.
If pressing is performed after applying 1 to 4.0 g/m2, mold galling will be further reduced. If the amount of the zinc phosphate treatment layer is less than 0.1 g/m2, the effect of reducing mold galling will be small, and if it exceeds 4.0 g/m2, the zinc phosphate crystals will become coarse and the paint adhesion will deteriorate. do.

In addition, it is necessary to contain 3 wt% or more of one or both of Ni and Mn in this zinc phosphate treatment layer, and this means that one or both of Ni and Mn must be contained in the zinc phosphate treated layer. This is because the inclusion of the two types improves the water-resistant adhesion, which is evaluated by the adhesion after the coating is immersed in ionized water to deteriorate the coating film. Note that Ni and Mn must be contained in a maximum amount of only 10 wt% in order to form zinc phosphate crystals. Therefore, Ni
and the content of one or two types of Mn is 3 to 1 Otvt
%.

Further, in addition to the zinc phosphate treated layer, a chromate treated layer, a resin layer, etc. can be used as the third layer as long as it does not adversely affect the pressing and painting processes.

A method for producing a Zn-Ni alloy plated steel sheet with excellent press workability and properties after painting according to the present invention will be briefly described.

In order to change the Ni content of the Zn-Ni alloy plating layer, it is necessary to control the Ni''/Zn'' ratio of the bath, current density, temperature, etc. The second layer can be formed by changing one or more of the above-mentioned control conditions, and by appropriately controlling one or two of the current density and temperature, the present invention can be formed using a single plating bath. Steel plates can be manufactured.

[Example] An example of a Zn-Ni alloy plated steel sheet having excellent press workability and properties after coating according to the present invention will be described.

Example 1 After deacidifying and pickling an O08t aluminum killed cold rolled steel plate, the first
A Zn-Ni alloy plating layer was applied as shown in the table.

The Ni content was controlled mainly by changing the Ni''/Zn'' ratio of the bath, and partly by changing the current density and temperature.

Various tests described below were conducted on these plating layers.

■Sliding Resistance In order to simulate mold galling during press processing, a sample was cut into 50 x 200 mm, and after being coated with a rust preventive coating, the sliding resistance (tensile load) was measured using the apparatus shown in Figure 2. The sliding resistance when mold galling does not occur is about 150 kgf. In Figure 2, the tensile speed is 500 mm/mi.
n, sliding length 150n+m, mold maintenance for each piece #800
Clean with sandpaper. H is the tensile direction,
S is sample, P is hydraulic pressure (surface pressure 178 kg/am”
), K is a sliding mold.

■ Salt spray test samples after painting were treated with zinc phosphate by immersion method (adhesion amount 2g/m
After cationic electrodeposition coating (film thickness: 20 μm), scratches were made on the coating film using a cutter knife, and a salt spray test was conducted for 800 hours, and evaluation was made based on the blistering width of the coating film from the scratches. It is desirable that the bulge width is 2n+n+ or less.

■ Exposure test samples after painting were treated with zinc phosphate by immersion (coating amount: 2 g/m) - cationic electrodeposition coating (film thickness: 20 μm) - intermediate coating (film thickness: 40 μm)
) - Top coat (film thickness: 40 μm) was applied to an automobile, and then scratches reaching the plating layer were made on the coating film using a cutter, and an exposure test was conducted for 6 months.

Samples were sprayed with saline once weekly. The evaluation was based on the degree of red rust generated from the scratches after 6 months.

Evaluation Degree ◎ No red rust ○ Red rust occurs in part of the flaw △ Red rust occurs in the entire flaw ℃
In this environment, 100 g of granite with a diameter of 7.9 to 11.1 mm was sprayed onto the surface of the coating film using an air jet at a pressure of 4 kgf/cm'.

The diameter of the part where the paint film was peeled off due to the collision with a stone was measured, and the maximum diameter was taken as the maximum peeling diameter of the paint film, and the impact peeling resistance was evaluated based on this diameter. When the maximum peeling distance is 5 mm or less, there is no problem in practical use.

Table 1 shows the results.

The steel plate according to the present invention shows good performance in all of the sliding resistance, salt spray test after painting, exposure test, and impact peeling resistance.

In the comparative example, a problem occurred in any of the above properties.Example 2: 0.8t aluminum killed steel. First layer Ni content: 8wt%
A Zn-Ni alloy plating layer with an adhesion amount of 15 g/m2 and a second layer Ni content of 13 wt%, an adhesion ffi 5 g/m'' were applied by electroplating, and then, Spray method zinc phosphate treatment (deposition amount 2.1 g/m', Ni+Mn 7.2 wt% in film)
I did it.

After applying rust preventive oil to this steel plate, the sliding resistance was measured using the measures shown in FIG. In this case, 10 consecutive steel plates of the same type were slid without cleaning the mold, resulting in a condition where mold galling was more likely to occur than in Example 1.

In the steel plate according to the present invention in this example, the sliding resistance during processing of 10 sheets was constant at 150 kgf, whereas in the case of no zinc phosphate treatment layer, the sliding resistance from the 4th sheet starts to increase, indicating that mold galling is occurring.

[Effects of the Invention] As explained above, since the Zn-Ni alloy plated steel sheet of the present invention having excellent press workability and properties after painting has the above structure, the sliding resistance is constant, and There is no mold galling, and it has excellent corrosion resistance such as salt spray test after painting, exposure test after painting, and impact peeling resistance after painting, and also has excellent press workability. It is something.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the ratio of the first layer and the second layer and the impact peeling resistance after coating, and FIG. 2 is a schematic diagram of a sliding resistance measuring device.夛1 Figure 12 Row Z? L-4; (t3 = /, ha town t and y/
,,")"4 r4tzndingryo 3 takuλme ni 11 daggers 2
ril ↑

Claims (2)

[Claims] (1) On a steel plate, a Zn-Ni alloy plating layer containing 3 to 10 wt% Ni as a first layer, and a Zn-Ni alloy plating layer containing 11 to 20 wt% Ni as a second layer thereon. It has a two-layer structure, and the ratio of the amount of the first layer attached to the amount of the second layer attached is 1:0.05 to 1, and furthermore, the first layer has a two-layer structure.
Total plating amount of layer and second layer is 10-80g/m^2
A Zn-Ni alloy plated steel sheet having excellent press workability and properties after painting. (2) On the steel plate, a Zn-Ni alloy plating layer containing 3 to 10 wt% Ni as a first layer, and a Zn-Ni alloy plating layer containing 11 to 20 wt% Ni as a second layer thereon. , Furthermore, on top of that, as a third layer, a three-layer structure of a zinc phosphate crystal layer containing a deposited amount of 0.1 to 4.0 g/m^2 and 3 to 10 wt% of one or both of Ni and P. and the ratio of the first layer adhesion amount to the second layer adhesion amount is 1:0.05 to 1, and the first layer adhesion amount is 1:0.05 to 1.
Total plating amount of layer and second layer is 10~80g/m^2
A Zn-Ni alloy plated steel sheet having excellent press workability and properties after painting.